Xen devel - Mar 2006 - RE: [PATCH] Re: [Xen-ia64-devel] Help? Red Hat fails, Suse/Debian both work fine

>From: Kouya SHIMURA
>Sent: 2006年3月3日 19:02
>Hi all
>
>Finally I found out the unstable problem about domU boot on ia64.
>Please see the comment in patch.
>
>This patch is one solution.
>Another solution is to ask the memory attributes to
>hypervisor but it looks excessive modification.
>
>Signed-off-by Kouya SHIMURA <kouya@jp.fujitsu.com>
>
>Best Regards,
>Kouya
Hi, Kouya,

Good finding for the cause, however several minor comments about your 
patch:
	- Be conservative when you want to modify common linux files, if 
without strong reasons.

	- Your change has potential issue. Your change actually makes all 
illegal addresses which is out of EFI memmap can get WB attribute, only
for accommodating another special page (store page) out of domU''s 
knowledge. I don''t think it''s right way to go.

	- See how x86 works. All special pages including store page, console 
page, start info, etc. are constructed within domU''s memory, and domU 
is aware of that. For XEN/IA64, you may want to steal last several pages 
from configured memory of domU. There''s an ia64 specific field named 
sys_pgnr (in xc_linux_build), which was targeted for this issue before 
however incomplete yet. Then you can pass to Xen and add one reserved 
EFI memmap entry to cover sys_pgnr pages with attribute WB at 
dom_fw_init. Since it''s reserved, domU won''t use it. However 
efi_mem_attributes can give ideal result you want. This workaround has 
no impact to xenlinux code, which may be quick solution. Of course, we 
may consider reconstruct more to make it cleaner in the future. ;-)

Thanks,
Kevin


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